Helicopter rotors comprising a reinforced plastics hub

ABSTRACT

A helicopter rotor has a reinforced plastics hub. Arms extend radially outwardly from the hub each arm carrying through, the intermediary of a sleeve, a blade. The arms are reinforced with fibres.

United States Patent 11 1 Bourquardez et a1.

1 1 Oct. 2, 1973 HELICOPTER ROTORS COMPRISING A REINFORCED PLASTICS IIUB{75] Inventors: Gaston Bourquardez,

Aix-en-Provence; Michel Jean Yves Gouzien, Bouc Bel Air; Ren Mercier,Aix-en-Provence, all of France [73] Assignee: Societe NationaleIndustrielle Aerospatiale, Paris, France 22 Filed: Feb. 2, 1912 21 Appl.No.: 222,871

[30] Foreign Application Priority Data Feb. 15, 1971 France 7104967 [52]US. Cl 416/134, 416/140, 416/141, 416/230 [51] Int. Cl. B64c 11/12 [58]Field of Search... 416/134, 135, 138,

[56] References Cited UNITED STATES PATENTS 3,026,942 3/1962 Cresap416/135 UX 3,280,918 10/1966 Drees et a1... 416/135 UX 3,384,185 5/1968Fernandez.... 416/134 UX 3,610,774 10/1971 Mouille 416/138 X 3,669,5666/1972 Bourquardez et a1. 416/134 FOREIGN PATENTS OR APPLICATIONS1,334,446 7/1963 France 416/134 Primary ExaminerEverette A. Powell, Jr.Attorneyl(arl W. Flocks [57] ABSTRACT A helicopter rotor has areinforced plastics hub. Arms extend radially outwardly from the hubeach arm carrying through, the intermediary of a sleeve, a blade. Thearms are reinforced with fibres.

10 Claims, 5 Drawing Figures PAIENTED 2 3.762.834

SHEET 2 [1F 3 PAIENTED 21913 3.762.834

v SHEET BUY 3 HELICOPTER ROTORS COMPRISING A REINFORCED PLASTICS HUBThis invention relates to a helicopter rotor comprising a reinforcedplastics hub enabling oscillatory move ments of the blades in the planeof rotor rotation, such oscillations being known as drag oscillations,and blade movements in planes perpendicular to the plane of rotorrotation, the latter movements being known as beat movements, to beproduced by static and dynamic bending of the reinforced plastics hubmaterial, whereas blade rotations around their longitudinal axis, suchrotations being known as pitch movements and serving to change the angleof blade incidence, are produced through the agency of an articulationwhich is provided between each blade and the flexible portion of the huband which enables the blade to rotate around its longitudinal axis.

Helicopter rotors devoid of heat and drag articulation are known, theblades of such rotors being mounted in a rigid hub by way of a pitchvariation hearing providing merely blade pitch variation. Of course, forsuch rotors to operate satisfactorily, either resilient intermediatemembers enabling each blade to perform the requisite beat and dragmovements must be interposed between the rigid rotor head and the bladeitself or the blades must be made of a glass-fibre reinforced plasticsimparting some flexibility to the blades for beat and drag purposes;also, and as French Pat. No. 1,595,587 discloses, blades of this kindcan comprise a neck-like footing or root part serving more particularlyfor adjustment of the natural beat and drag frequency of the rotatingblades.

Rotors of this kind have a number of severe disadvantages, moreparticularly at high speeds of travel; the flexible elements are fairlyfar away from the hub centre, with the result that unstabilising torquesmay be produced when the rotor disc is tilted by a gust of wind. Placingthe pitch articulation forwards of the flexible elements of the bladeintroduces interfering incidence variations due to coupling between beatand drag deformations. Such pitch variations may cause extreme fore andaft pitching instability at high speeds and be the cause of highvibratory excitations.

The invention obviates these disadvantages.

According to an important feature of this invention, the hub comprisesarms which are provided to the same number as there are blades and whichare reinforced with substantially radial high-mechanical strength fibregroups whose cross-section near the hub is flat in the rotor plane, suchcross-section merging into a substantially radial cylindrical portion,the same bearing a sleeve on which an annular member rigidly secured toeach blade by appropriate securing means rotates.

Preferably, the centrifugal force acting on the blade is in known mannerborne by an elongated straight element secured to the blade and to thearm and adapted to withstand longitudinal tension but adapted to twist.

Advantageously, the elongated element takes the form of a group of glassfibres which are coaxial of the cylindrical portion. Preferably, thegroup of fibres is integral with the hub framework and forms theterminal portion of a group incorporated in such framework. There istherefore no need for anything to be secured to the hub, securing to theblade being by means of the shaping of the blade outer end.

Preferably, the axial group or bunch is cylindrical and enveloped in avulcanized elastomer; it can be separated from the remainder of the hubby a plastics antifriction sleeve, e.g., of polytetrafluoroethylene.

To reduce flight vibrations known as air resonance and to limit dragtorques when the drag resonance is passed through a take-off and atstoppage of the rotor, the hub comprises, with advantage drag damperswhose operative movement can be small, since the movements of theflexible arms of the hub are relatively small.

Since the central portion of the moulded hub is contained in a metalcasing, the drag dampers can be disposed between securing points securedto the sleeves borne by the cylindrical portions of the arms and to thecasing in the space between two consecutive blades.

As compared with articulated metal blades, the hub according to theinvention, which operates similarly to such hubs, is very simple, andso, taken together with the reduced number of delicate parts required,including rolling bearings and metal parts working in fatigueconditions, overall reliability is improved, weight and cost are reducedand maintenance greatly simplified. Also, using glass fibres gives thehub very great fatigue strength, plus a safety advantage in thatdamage'occurs progressively and never abruptly and is accompanied bydelamination which is visible for a very long time before final rupture.

A useful feature of the hub according to the invention is that it can beassociated with a wide variety of blades, e.g., with metal or reinforcedplastics blades.

Also, an advantage which the rotor according to the invention has overrotors which are devoid of beat and drag articulations and where thenecessary flexibility is in the actual blades, more particularly attheir root, is that a rotor having a hub according to the invention canhave flexible beat elements nearer the centre of the hub, thus providinga strong stabilising effect on the rotor, more particularly in windgusts.

The angle of blade incidence of such a rotor is not affected by hub beatand drag deflections, since the pitch articulation is interposed betweeneach blade and the deformable element of the hub. This feature obviatesthe pitching instability and high vibratory excitation from whichhelicopters having flexible blades suffer when travelling fast. I

The accompanying drawings show how the invention can be carried intopractice.

In the Drawings:

FIG. 1 is a plan view, with parts removed, of a first embodiment of theinvention;

FIG. 2 is a section on the line II II of FIG. 1;

FIG. 3 is a section similar to FIG. 2 through an alternative form of theelements disposed between the blade and the flexible arm;

FIG. 4 is an exploded perspective view of a hub embodiment of the kindshown in FIG. 3, and

FIG. 5 is a view in horizontal section of another constructionalvariant.

The hub shown in FIGS. 1 and 2 mainly comprises a central portion 1 madeof high-strength fibres, e.g., of glass, impregnated with syntheticresin and arranged star-fashion to form around the axis of rotorrotation as many flexible arms 2 as the rotor has blades. To form thearms, the fibres, which are continuous from any arm to the next andwhich are curvilinear in the central portion 3, are so disposed that,without any change in superficial area, the cross-section of each armgradually changes from a substantially oval shape in root zone 4, withthe flattened zone extending perpendicularly to the hub axis, into acircular shape at end 5.

Preferably, the central portion 3 is reinforced by a covering 3a in theform of a number of layers of resinimpregnated glass cloth so as to formthe hub body and enable the hub to be secured to the top of shaft '6,which flares out to form a collar 6a, through the agency of two metalpartial shells 7, 8 which encase the central portion 3 and which arerigidly secured to one another and to collar 60 through the agency ofscrew-threaded spindles 9 retained by nuts 10 disposed between the arms.

In the central stellate space left free by the fibre groups extendingbetween consecutive arms a rigid plastics filling 11 is provided arounda bush or the like 12 which is used to enable a tool to be positioned orfor electric wiring.

. Preferably, the circular portion 5 is thickened and strengthened overa length A at each arm end by the introduction of glass cloth members 13between the glass fibre layers. The resulting terminal portion 14 isthen mechanically strong enough to withstand stressing in alldirections. Disposed in the central space of the circular portion 5 is arigid plastics filling identical to what is used in the central internalportion of the hub body.

The portion 14 receives the connecting means between the arm and theblade root, such means providing a transfer into the arm of the forcesand moments produced by the rotating blade (beat, drag, centrifugalforces) and a pitch articulation which, under the control of anappropriate control lever, enables the pitch of each blade to be variedby pivotting around the geometric axis of the portion 14. To this end,the same is drilled after polymerisation. A metal ring 16 is introducedinto the aperture and centred by an appropriate tool, and in a singleworking step the ring 16 and a steel outer cylindrical bush or the like15, which extends right'around the portion 14 and thus can transmittransverse forces and moments, are stuck on. The longitudinalcentrifugal tension is applied to ring 16 by way of a steel spindle orshaft 16a extending therethrough, the ring 16 compressing the portion 14so that the same operates in shear stress.

The pitch articulation can take the form e.gof a rolling-bearing typeabutment l7 interposed between a hoop or collar or the like 18 slid intosleeve 15 and retained by spindle 16a the end of the hoop forming theinner raceway for the rollers 17 and a sleeve 19 whose end forms theouter raceway. Through the agency of a plain or needle bearing 20,sleeve 19 also rotates on the extension of bush 15, with sealingtightness between the same and the sleeve 19 provided by a gasket 21.The complete bearing 20 is lubricated either with grease or by oilimmersion and comprises appropriate lubrication nipples.

On the side near blade 25, sleeve 19 has a collar 19a for the securing,by means of a ring of nut-and-bolt connections 22, a blade brace or thelike 23 terminating in a double yoke which, through the agency of twospindles or pins or the like 24, serves to retain blade 25.

Secured to the inside of sleeve 19 by nuts and bolts is a lever 26 whichis connected to the helicopter control system for blsde pitch variationpurposes.

In this construction, centrifugal force acting on the blade istransmitted to the arm 2 by the conical abutment comprising the rollers17.

A known kind of short-travel drag damper 27 is disposed between, on theone hand, the central hub part, by way of a brace or the like 28 securedto the partial shell members 7, 8 through the agency of spindles or thelike 9, and, on the other hand, to the end of each flexible arm by wayof a lever 29, which extends and is secured to the member 15.

FIG. 3 shows an alternative form of connection between the end of theflexible arm and the blade brace. In this construction the stationarybush 15 comprises two inner raceways 30, 31 for two needle bearings 32,33; a brace 36 (which has, on the side near the blade, a yoke receivingthe two members 24) is shaped, on the side near the hub centre, as acylindrical member extending around the member 15 and forming outerraceways for the needles 32, 33. A pitch control lever 26 is secured byscrew-threaded fastenings to the end of the cylindrical portion whichextends around the member 15. Disposed between the brace 36 and thecylindrical portion 14 is a known kind of twistable element 34 such asabunch of steel strips or an element of wound steel wires. Such elementis received inside portion 14 and is adapted to transmit centrifugalforce while allowing the blade to rotate relatively to the hub. Element34 is retained by a pin or spindle or the like 35 in a recess in member36 and is retained on the end of the flexible arm by spindle or pin orthe like 16a. Advantageously, the element 34 is embodied as a bunch ofvery strong fibres covered in flexible elastomer and built into the armat manufacture thereof. This suggestion helps to reduce the cost of thehub by removing the usually very costly external elements required todeal with centrifugal forces, as well as reducing overall weight byusing lightweight glass-elastomer laminates instead of parts made ofmetal more particularly steel.

The variant shown in FIG. 5 shows how the strut o the like which has towithstand centrifugal force can be embodied as a bunch of strong fibresimpregnated with flexible vulcanized elastomer, such bunch or groupforming part of the glass fibre framework of the hub.

In this case, a portion 37 of hub-reinforcing fibres is shaped to form acylinder 38 coaxial of the cylindrical portion 14 and impregnated withflexible vulcanized elastomer. The outer free end 39 of cylinder 38 isimpregnated with a strong polymerisable synthetic resin to form aconnecting element for the blade 25. As shown, a head through which apin or the like 40 providing a connection to the blade extends can beprovided in this way.

If required, the same end can be shaped as a conical head which engagesin a recess in blade 25. 4

The cylindrical portion 38 which forms a torsion element can be of alength equal to half the total length of the arm 2. Preferably, portion38 is disposed beyond that part of arm 2 which is near the hub and whichexperiences bending due to beating and drag. Advantageously too, portion38 is included, at least mostly, in the member 15 forming a bearing forthe blade.

Twist deformation of the cylindrical portion 38 is assisted by a teflonsheath 41.

To construct a hub of this kind, the cylindrical portions 38 aremanufactured first and covered with their teflon sheath, whereatter thecomplete hub with its glass fibre framework comprising the cylindricalportions 38 is moulded after impregnation with a resin.

In the embodiment shown in FIG. 5 the drag dampers 27 are secured atboth their ends to lugs 29 on members 15.

The invention is of use for all helicopters comprising one or more liftrotors.

We claim:

1. A rotor construction comprising a one-piece starshaped moulded rotorhub substantially made of bundles of mineral filaments agglomerated by apolymerized synthetic resin, each bundle extending from the end of onestar arm to the end of the next one, each star arm having near the hubaxis, in the star plane, a flattened cross-section merging into acylindrical substantially radial end portion; a sleeve, surrounding eachsaid cylindrical portion and secured thereto, having at least a laterallug at the end directed towards the hub axis; an elongated drag damperin said star plane, one end of which is secured to said lug and theother to the hub towards one of the next star arm; a blade having abushing engaging each said sleeve; roller means between said bushing andsleeve and means adapted to withstand centrifugal force for securingsaid blade to said arm.

2. The improved rotor of claim 1 wherein the said end cylindricalportion is thickened by the inclusion of shapes in strong fibre clothscoaxially of the group of axial fibres of the cylindrical portion.

3. The improved rotor of claim 1, wherein said means to withstandcentrifugal force is a straight element which withstands tension butwhich can twist and which is disposed axially in the cylindrical portionand whose ends are secured, on either side of the cylindrical portionwhich bears the sleeve, to the arm and to the blade.

4. The improved rotor of claim 1, wherein one of the two ends of saiddrag damper is secured to a casing containing the central part of thehub in the gap between two blades.

5. The improved rotor of claim 2, wherein said means to withstandcentrifugal force is a straight element embodied by a group of strongfibres encased in a flexible vulcanized elastomer.

6. The improved rotor of claim 5, wherein the group is a terminalportion of the hub-reinforcing fibre groups.

7. The improved rotor of claim 5, wherein the fibre group is isolatedfrom the cylindrical portion by a flexible antifriction plastics sheath.

8. The improved rotor of claim 6, wherein the outer end of the group isencased in hardened synthetic resin and shaped for connection to theblade.

9. The improved rotor of claim 6, wherein the terminal part of the grouphas a length substantially equal to half the total length of the arm.

10. The improved rotor of claim 6, wherein the terminal part of thegroup extends mainly in the arm part comprising the cylindrical portionaround which the sleeve extends.

1. A rotor construction comprising a one-piece star-shaped moulded rotorhub substantially made of bundles of mineral filaments agglomerated by apolymerized synthetic resin, each bundle extending from the end of onestar arm to the end of the next one, each star arm having near the hubaxis, in the star plane, a flattened cross-section merging into acylindrical substantially radial end portion; a sleeve, surrounding eachsaid cylindrical portion and secured thereto, having at least a laterallug at the end directed towards the hub axis; an elongated drag damperin said star plane, one end of which is secured to said lug and theother to the hub towards one of the next star arm; a blade having abushing engaging each said sleeve; roller means between said bushing andsleeve and means adapted to withstand centrifugal force for securingsaid blade to said arm.
 2. The improved rotor of claim 1 wherein thesaid end cylindrical portion is thickened by the inclusion of shapes instrong fibre cloths coaxially of the group of axial Fibres of thecylindrical portion.
 3. The improved rotor of claim 1, wherein saidmeans to withstand centrifugal force is a straight element whichwithstands tension but which can twist and which is disposed axially inthe cylindrical portion and whose ends are secured, on either side ofthe cylindrical portion which bears the sleeve, to the arm and to theblade.
 4. The improved rotor of claim 1, wherein one of the two ends ofsaid drag damper is secured to a casing containing the central part ofthe hub in the gap between two blades.
 5. The improved rotor of claim 2,wherein said means to withstand centrifugal force is a straight elementembodied by a group of strong fibres encased in a flexible vulcanizedelastomer.
 6. The improved rotor of claim 5, wherein the group is aterminal portion of the hub-reinforcing fibre groups.
 7. The improvedrotor of claim 5, wherein the fibre group is isolated from thecylindrical portion by a flexible antifriction plastics sheath.
 8. Theimproved rotor of claim 6, wherein the outer end of the group is encasedin hardened synthetic resin and shaped for connection to the blade. 9.The improved rotor of claim 6, wherein the terminal part of the grouphas a length substantially equal to half the total length of the arm.10. The improved rotor of claim 6, wherein the terminal part of thegroup extends mainly in the arm part comprising the cylindrical portionaround which the sleeve extends.